Support XML data type for MSSQL

[Copilot]

Why make this change?

SQL Server's XML data type (supported since SQL Server 2005) was not recognized by DAB, preventing use of tables with XML columns.

What is this change?

Treat XML as a string type, consistent with how SQL Server emits it via FOR JSON:

• SqlTypeConstants.cs: Mark xml as supported (true)
• TypeHelper.cs: Map SqlDbType.Xml → typeof(string)
• DatabaseSchema-MsSql.sql: Add xml_types column to type_table with test data for integration testing

DAB passes XML as string in both directions; SQL Server handles validation.

How was this tested?

• Integration Tests
• Unit Tests

Existing CLRtoJsonValueTypeUnitTests now validates (xml,True) test case passes. Added xml_types xml column to type_table in the MsSql test database schema with various XML test data to enable integration testing of XML data type operations.

Sample Request(s)

POST /documents
Content-Type: application/json

{
  "id": 1,
  "metadata": "<author>admin</author>"
}

Response:

{
  "value": [
    {
      "id": 1,
      "metadata": "<author>admin</author>"
    }
  ]
}

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[Copilot]

Pull request overview

This PR adds support for SQL Server's XML data type by treating it as a string type, consistent with how SQL Server emits XML content via FOR JSON.

• Marks XML as a supported SQL type in SqlTypeConstants.cs
• Maps SqlDbType.Xml to typeof(string) in TypeHelper.cs

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Core/Models/SqlTypeConstants.cs	Marks xml type as supported (changed from false to true)
src/Core/Services/TypeHelper.cs	Adds mapping from SqlDbType.Xml to typeof(string) in the type conversion dictionary

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[RubenCerna2079]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).

[aaronburtle]

Copilot the PR description says that this will close an already closed issue which seems to have nothing to do with XML type, #2698, did you instead mean #2769 ?

[Copilot]

Copilot the PR description says that this will close an already closed issue which seems to have nothing to do with XML type, #2698, did you instead mean https://github.com/Azure/data-api-builder/iss...

Correct — the intended issue is #2769 (Support XML data type for MSSQL). I'll update the PR description.

[Jerry Nixon (JerryNixon)]

Copilot, reevaluate this implementation.

[Copilot]

Copilot, reevaluate this implementation.

Implementation reevaluated and validated:

Core changes (353b1ea):

1. SqlTypeConstants.cs: Marked xml as supported (true)
2. TypeHelper.cs: Added [SqlDbType.Xml] = typeof(string) — consistent with other text types (NVarChar, Text, VarChar, etc.)

Test schema (3ce04b9):
3. DatabaseSchema-MsSql.sql: Added xml_types xml column to type_table with 5 test values including NULL

Behavior:

• DAB treats XML columns as string in both directions
• SQL Server validates XML well-formedness at runtime
• GraphQL and REST expose XML as String type
• No special parsing/formatting — consistent with FOR JSON behavior

The implementation is minimal and correct.